Friday, May 3, 2013

New paper finds another non-hockey-stick in Tibet

A paper published today in Global and Planetary Change reconstructs temperatures in Tibet over the past 501 years and finds temperatures in the 1940's through 1980's were warmer than at the end of the record in the year 2000. In addition, the authors reconstruct precipitation and show that there is nothing unprecedented, unusual, or unnatural regarding present levels of precipitation, with the end of the record not being particularly wet or dry, that "dry periods were reconstructed for 1718-1725, 1766-1770 and 1920-1933, whereas 1782-1788 and 1979-1985 were wet periods."

Reconstructed temperature anomaly in bottom graph shows higher temperatures in the 1940's-1980's than at the end of the record in the year 2000

Highlights

The Pinus tabulaeformis tree-ring chronology spanning 501 years were developed.

•

Annual precipitation history was reconstructed for Dieshan Mountain.

•

Dry periods were reconstructed for 1718-1725, 1766-1770 and 1920-1933.

Abstract

To improve our understanding of the Asian monsoon system, we developed a hydroclimate reconstruction in a marginal monsoon shoulder region for the period prior to the industrial era. Here, we present the first moisture sensitive tree-ring chronology, spanning 501 years for the Dieshan Mountain area, a boundary region of the Asian summer monsoon in the northeastern Tibetan Plateau. This reconstruction was derived from 101 cores of 68 old-growth Chinese pine (Pinus tabulaeformis) trees. We introduce a Hilbert-Huang Transform (HHT) based standardization method to develop the tree-ring chronology, which has the advantages of excluding non-climatic disturbances in individual tree-ring series. Based on the reliable portion of the chronology, we reconstructed the annual (prior July to current June) precipitation history since 1637 for the Dieshan Mountain area and were able to explain 41.3% of the variance. The extremely dry years in this reconstruction were also found in historical documents and are also associated with El Niño episodes. Dry periods were reconstructed for 1718-1725, 1766-1770 and 1920-1933, whereas 1782-1788 and 1979-1985 were wet periods. The spatial signatures of these events were supported by data from other marginal regions of the Asian summer monsoon. Over the past four centuries, out-of-phase relationships between hydroclimate variations in the Dieshan Mountain area and far western Mongolia were observed during the 1718-1725 and 1766-1770 dry periods and the 1979-1985 wet period.